PrologueI enjoyed building the Great Planes Spirit 100 considerably. This is a good intermediate sailplane kit, and despite its detractors, it can teach you quite a bit about how to fly. In addition, it has the advantage of being much less expensive than the next level of sailplane model. Ultimately, it was unflyable in Southern Maryland. I don't have access to the space required for a full launch, and there just aren't enough sailplane enthusiasts to make it enjoyable. With my discovery of electric flight, it became the first project on my list to convert - and was rechristened the Esprit 100.
14 February, 2006
Finishing the Spirit 100
I tried a lot of configurations without avail (receiver under wing, wires over and under servos). I eventually settled on getting the switch out of the way with a Du-Bro switch harness and charging jack behind the servos (mighty tight installation, but a good spot for it).
After this was done, I had little need to frequently remove the hatch, so I ran the wing servo connections (should have used a bundled cable) and the battery lines in between the polystyrene cockpit and the balsa frame. After I plugged in the Rx, I had just enough wiggle room to get the rubber band back in place that holds the whole thing down.
After a few flights, I will likely add a spruce bolt plate and drop a 10-32 wing bolt through the hatch where it attaches to the forward wing bulkhead. Tomorrow (with any luck), I'll rehinge those sloppy ailerons and be ready for business.
19 February, 2006
I hate hinges
So today I go and get some balsa and some hinges, and then I get the left aileron back on. I go to reconnect the servo, and I notice that I am still having this horrible problem with center point drift. I assumed that it was a problem with the radio, and that I was trying to do too much mixing. Well, I played with it for a while, and noticed that at the top of the aileron throw, the servo was bouncing, and after each bounce, it would lose a little ground against center.
Each time I would recenter it, and neutralize the trim electronically. Then the problem would continue, until it had slipped so much that it couldn't even be centered any more. Thats when I noticed that the horn was slipping against the servo itself. I pulled it apart, and sure enough, I was using a Futaba horn with a Tower servo. The shaft of the servo is the right size for the horn, but the teeth within the horn are the wrong shape.
I ended up going back to the hobby store and buying a pack of DuBro horns that are for Tower servos. Now I don't seem to be having any problem with it. Let this be a lesson (that I obviously needed to learn). Keep your servo horns segregated by manufacturer. That mistake could have cost me a glider!
After completing the left aileron and the flap servo horn changes, I just didn't have anything left to do the right aileron. Thank goodness tomorrow is President's Day. Thank goodness that I have such a great local hobby shop (Doug's Hobby ).
The moral of this story is that nothing can make you feel like an idiot quite like actually being an idiot.
20 February, 2006
Preparing the Spirit...
I immediately realized that the servo arm on the flap servo was too long, it was hitting the ballast box. So I took the wing apart and changed the servo arm. It was at this point, that I noticed (to my horror) that the flap servo had no position control. This could only mean one thing, and a dissection of the servo revealed that one of the gears had indeed shed its teeth.
It was off to the hobby store to find a replacement, and luckily they had one last Hitec (no box, no horns and no grommets). I snatched it up for the deal that they offered and ran back home.
Finally I completed the plane, and with all of the servo problems now fixed, the radio mixing is a dream.
As would be expected, it snowed last night, so now I have to wait some more for a trial flight.
That gives me time to start my next project: the Tern 2VS.
08 September, 2006
I had an E-Flite 400 brushless outrunner at home (great motor), and while this motor doesn't quite provide the 50 W/lb desired for a sailplane motor, I thought that it would be ok, especially with others' experience. Besides, I didn't want a hotliner, I just wanted something that would climb a few times on a charge.
So, my initial pass at equipment looked something like this:
1. Brushless 400 motor with folding prop.
2. Thunder Power 1320 LiPos in a 3S-2P configuration running at 11.1 V and 2640 MAh
3. A separate 1000 MAh Rx pack to provide the amperage to run the servos and give endurance for long flights
4. My Futaba R149 (it needs some test flights before it gets put in the Tsubame anyway)
I did some weight and balance calculations, and it looked like I could get all this mounted for roughly the same weight I have now. The practicality of that might not be so true. I also have to find a way to provide some airflow through the motor/battery compartment for the ~2 minute power climbs.
More to come...
Today, I set out with a plan. I wanted to fabricate a firewall that, with the use of a Graupner spinner, would roughly maintain the front lines of the Spirit. I started out by picking a cut line and taking the balsa block off the nose. I then machined out a cavity in the remaining wood that would enable the motor to spin.
After this, I fabricated the firewall using a piece of 3/16 ply bonded to a piece of 3/32 ply. I used this to give me the right spacing off the existing first bulkhead of the Spirit. I drilled this for the motor mount and used 4-40 blind nuts for the anchors.
Once I got this done, I ground the first bulkhead down so that I could bond in the firewall. I kept the edge of the bulkhead to use as a positioning guide, but machined enough away so that the bolts would clear and I wouldn't have to try and cut any more once the assembly was done.
Then I could bond the firewall in place. I put tape over the back of the blind nuts so that I wouldn't fill the threads with epoxy. I wet down the edges of the fuse with 20 minute epoxy and then added more epoxy with microballoons once the bulkhead was in place. After the cure, it was a simple matter of bolting the engine on.
Finally, I had to cut quite a bit of the cockpit away under the canopy to provide some air space for cooling air to flow around the motor and through the battery compartment. When complete, this provided a functional, if ugly, method of ramming cooling air through the forward fuse. I tried to compensate for the ugliness by painting the canopy silver.
Of course, like all good tinkerers, I just couldn't wait to see the fruits of my labor. I strapped an APC 11x4 prop to the front of the motor, dropped a 3S LiPo on the ESC, and let it rip on the table of my bandsaw. Two things were learned from this. First, that we surely have enough thrust and second, that we have plenty of cooling. Just to validate this, I will do some static runs of several minutes with thermocouples in the battery bays. Should be fun!
Tomorrow's episode will cover my new hatch hold downs and my current approach to radio mixing.
09 September, 2006
I finished the front end, mounting a ring on the nose ahead of the engine and rounding the fuse to meet it. This would help ensure that there wasn't an odd looking transition between the fuse and the spinner.
You can see in the middle of the bay behind the motor (where the flight pack will go) that I have included a button magnet to hold down the canopy. With four of these (two on the fuse and two on the canopy), there is no additional hold down method required, but I will likely put a rubber band on the canopy just in case.
After mounting the canopy, I took a picture of the new profile of the front end. As you can see, I removed quite a bit of covering to round the nose properly. I am going to redo all of the covering in the front end to try and even things up a bit.
Finally, this morning we headed up to Waldorf to check out the outdoor supply and army surplus store. I picked up a 0.30 cal ammo box there to store LiPos for transport. For $4, a pretty cheap way to get some piece of mind. The boxes lock and are waterproof too.
This was followed by a 2 minute cooling period, and another run of 5 seconds at max power and 120 seconds at 5/6 power a 2F change was measured at the battery.
I then removed the thermocouples and ran alternate 2:05 run/rest cycles (using 120 seconds at 5/6 power). I stopped after completing 6 more cycles (for a total of 8). All this was done with a single Thunder Power 3S 1320 mAh pack.
With the correct propellor, a 2 minute climb should net somewhere between 500 and 1000 feet. This should translate into 3-5 minutes of gliding with no lift. With two packs, it should be possible to fly for 70 minutes on a single 3S-2P charge.
I had better bring a chair.
An update. I charged the single LiPo cell that I used for the battery tests, and apparently, only 62% of the capacity was used for those eight runs. When I redid the calculations for this new battery figure, it seems possible to get a flight time of nearly 3 hours!
18 September, 2006
Rechristening the Spirit
Once I got the prop on, I balanced the plane with just a few ounces of lead in the battery compartment. The plane ended up tipping the scales at 73 ounces, with the engine producing 26 ounces of thrust (at roughly 140 W). That comes out to a power loading of 32 W/lb, a wing loading of 11.5 oz/sq ft and a T/W ratio of 0.36:1. It won't be a hotliner by any means, but I hope that it will provide some climbing power.
I had a local auto customizing shop (D&G Kustom) cut some vinyl lettering for me, and I rechristened the airplane the Esprit 100.
I was especially pleased with the way that the tail numbers looked when applied over the rudder and fin.
EpilogueThis story is far from over, how could I write the Epilogue yet?
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